Increasingly stringent specifications on motor fuel sulfur levels pose a refining and distribution challenge. In the future, these specifications are expected to tighten further with some fuels ultimately being required to have near-zero wppm sulfur levels. Current refinery hydroprocessing technology is not economical for meeting such near-zero ppm sulfur specifications. Thus, new desulfurization technology is needed to more economically reach those levels. Sodium has long been recognized as a desulfurizing agent for hydrocarbon materials, but safety concerns, among others, have prevented the development of a commercial sodium-based desulfurization process.
Legislation in recent years in many countries around the world requires that diesel and gasoline sulfur levels be typically less than 10's of wppm. It is likely that clean fuels with about 10 wppm or less sulfur will be legislated in most parts of the world.
In addition to ultra-clean mogas and diesel regulations, new technological developments are anticipated to create needs for liquid hydrocarbon fuels with less than 1 wppm sulfur. Currently, significant research and development effort is underway to develop fuel-cell powered automobiles. It is anticipated that these fuel-cell powered vehicles will begin to replace conventional internal combustion and diesel engines within the next several decades. Such fuel-cell vehicles may deploy an onboard catalytic reformer to generate hydrogen from gasoline. The fuel cells and various catalyst systems required to produce hydrogen are very susceptible to poisoning by sulfur and will require hydrocarbon fuels with less than about 1 wppm sulfur.
Traditionally, refineries use hydroprocessing to lower sulfur levels in hydrocarbon streams. While commercially attractive and widely used to meet sulfur specifications, hydroprocessing is not commercially viable for meeting the very stringent sulfur specifications of the future. For example, complete removal of the refractory sulfur species, such as substituted dibenzothiophenes, from distillate feedstreams requires severe hydroprocessing conditions that are economically unattractive. To achieve very low levels of sulfur in distillate products, such as diesel fuels, significant new investment in high-pressure hydroprocessing and new hydrogen facilities would be needed. Additionally, the octane loss associated with severe hydrotreating of mogas pool feedstreams limits the production of ultra low sulfur fuels by conventional hydroprocessing methods. Even with advanced hydrotreating technologies, there may be a need for an alternative desulfurization technology to allow more flexibility and control in refining operations. Thus, there is need for an alternate desulfurization process that can produce motor fuels containing near-zero sulfur.